1. Field of the Invention
The present invention relates to an apparatus for generating a uniform magnetic field and more specifically to an arrangement in which a plurality of small spheres of magnetic material are provided on magnetic pole pieces in order to finely adjust the uniformity of the magnetic field produced. The present invention has found an extensive application wherein a highly uniform magnetic field is required, such as in nuclear magnetic resonance computer tomography (NMR-CT).
2. Description of the Prior Art
The uniformity of the magnetic field which is used in connection with NMR-CT has a very large effect on the clarity and resolution of a NMR-CT image. Accordingly, it is of extreme importance that the magnetic field uniformity is increased to the maximum possible limit.
In order to improve the uniformity of such a magnetic field, it has been proposed to provide, within a yoke, a pair of opposed circular disc type permanent magnets each of which is magnetized in a direction of thickness and each of which is provided with a pole piece thereon. The pole piece has an annular projection about the periphery thereof.
It has also been proposed to dispose additional members (both fixed and movable) about the perimeter of the annular projections in order to deflect the outwardly curving lines of magnetic flux which tend to be produced at the outer peripheral zones of the magnets, inwardly in an effort to straighten the same to the greatest possible degree.
However, these efforts have not met with particular success in that the compensating or correcting members are provided about the periphery of the magnetic poles. In other words, the magnetic field correcting members are positioned remote from the uniform magnetic field produced, and hence are unable to effectively adjust or correct the magnetic field.